what hints did the writer provide earlier that zaroff would force rainsford into contest ?

Quotes from the text:

"Oh, it isn't here naturally, of course. I have to stock the island."

"I wanted the ideal animal to hunt," explained the general. "So I said, `What are the attributes of an ideal quarry?' And the answer was, of course, `It must have courage, cunning, and, above all, it must be able to reason."

".....I'll wager you'll forget your notions when you go hunting with me. You've a genuine new thrill in store for you, Mr. Rainsford."

"Dear me, what a righteous young man you are! I assure you I do not do the thing you suggest. That would be barbarous. I treat these visitors with every consideration. They get plenty of good food and exercise. They get into splendid physical condition. You shall see for yourself tomorrow."

"Ah, indeed?" the general inquired solicitously. "Well, I suppose that's only natural, after your long swim. You need a good, restful night's sleep. Tomorrow you'll feel like a new man, I'll wager. Then we'll hunt, eh?

and finally;

"The bed was good, and the pajamas of the softest silk, and he was tired in every fiber of his being, but nevertheless Rainsford could not quiet his brain with the opiate of sleep. He lay, eyes wide open. Once he thought he heard stealthy steps in the corridor outside his room. He sought to throw open the door; it would not open."

what is th significance of the initial quote and the fourth and the fifth ?